This invention relates to apparatus for detecting the presence of objects within a boundary area, for example, passengers or objects between the doors of an elevator car.
In typical elevator installations where the cars are operated automatically, it is common practice to provide apparatus to protect passengers against injury from the automatically closing doors. Such apparatus frequently include arrangements employing antennae located along the door edges in order to detect the presence of a person or object. Detection is accomplished by sensing the change in capacity brought about between the antenna and ground caused by the proximity of the person or object to the antenna. Such apparatus may be utilized to halt the door movement or cause continuous door retraction until the path is clear. Apparatus of this type are disclosed in the following patents which are commonly owned herewith: U.S. Pat. No. 2,601,250 to Bruns et al for a SAFETY SYSTEM FOR DOORS, which issued on June 24, 1952; U.S. Pat. No. 2,720,284 to Gallanty for ELEVATOR DOOR CONTROL MECHANISM, which issued on Oct. 11, 1955 and U.S. Pat. No. 3,018,851 to Diamond et al for CONTROL MECHANISM FOR DOORS, which issued Jan. 30, 1962, and U.S. Pat. No. 3,743,058, also to Diamond, which issued on July 3, 1972.
As disclosed in the patent to Bruns, each antenna is coupled to an electronic gas tube which fires as a result of increased capacitance between the antenna and ground. When the tube fires, the door may be stopped or reversed by suitable door motion controls until the path is clear.
In the patent to Gallanty, antennae are arranged in a pattern along the door edges to minimize erroneous door movement by compensating for some of the field disturbances arising from external elements, such as the hoistway doors and door jams.
In the first identified patent to Diamond, an arrangement is disclosed for improving the operation of the Gallanty system, by improving its immunity to disturbances from external elements. Each antennae forms one arm of a balanced bridge detector that includes variable capacitors which are adjusted so that the bridge is balanced when there is no object in the detection area of the antennae. An object entering the detection area produces increased capacitance, which causes a bridge unbalance and the consequent generation of a bridge output signal whose level is proportional to the change in capacitance. The output signal, which thus indicates the presence of an object between the doors, may be coupled to the door motion control apparatus to control door movement accordingly. The antennae may be arranged in a selected pattern around the door to minimize blind spots.
Environmental or ambient factors, such as humidity and temperature, frequently produce day to day and floor to floor changes in capacitance in elevator systems. As a result of this, balanced bridge systems may generate erroneous door motion control signals, causing the doors to move randomly or hang up on certain floors. Since car motion is typically geared to door position, the car will be immobilized, causing service interruption. Such effects may be prevented, in some instances, by bridge recalibration to null out any unbalance due to such factors. But where these factors change frequently, recalibration is not feasible. One example of this are the summer months, which typically are characterized by wide variations in humidity and temperature. Moreover, in air-conditioned buildings the temperature and humidity may vary dramatically at different times of the day as a result of controlled air-conditioning use. Where the humidity varies considerably, the capacitance sensed by the antennae similarly varies, and, thus, under those circumstances it is virtually impossible to achieve reliable bridge balancing. Consequently, when such conditions are encountered, the elevator system is especially susceptible to erroneous door movement and the deteriorated system speed, which results when the cars are unpredictably immobilized at certain floors.
The later patent to Diamond describes a self-adjusting proximity detecting apparatus which focuses on improving the operation of the system shown in the first Diamond patent principally by nulling out the balance bridge output signal caused by humidity and external elements--other than people and objects in the vicinity of the antennae. While this system offers significant improvement, it may be adversely effected by environmental and structural effects which may saturate the detector output, causing the detector to be blinded to the presence of an object, and thus rendering the detector ineffective. The bridge detector gain may be lowered to remedy this, but lowering the gain reduces detector sensitivity. With reduced sensitivity only objects which are very close to the doors are detectable; consequently, the doors may have to close on an object before it can be detected; the doors are then retracted, since this increases amount of door motion at each stop and it decreases overall system speed. Conversely, high sensitivity increases system speed because there is less unnecessary door motion.